Global Climate Change Calamity: Large Sections of Australia’s Great Reef Are Now Dead #greatbarrierreef #climatechange #globalcalamity

Severe bleaching last year on the northern Great Barrier Reef affected even the largest and oldest corals, like this slow-growing Porites colony.Credit Terry Hughes et al./Nature

“Climate change is not a future threat,” Professor Hughes said. “On the Great Barrier Reef, it’s been happening for 18 years.”

Corals require warm water to thrive, but they are exquisitely sensitive to extra heat. Just two or three degrees Fahrenheit of excess warming can sometimes kill the tiny creatures.

SYDNEY, Australia — The Great Barrier Reef in Australia has long been one of the world’s most magnificent natural wonders, so enormous it can be seen from space, so beautiful it can move visitors to tears.

But the reef, and the profusion of sea creatures living near it, are in profound trouble.

Huge sections of the Great Barrier Reef, stretching across hundreds of miles of its most pristine northern sector, were recently found to be dead, killed last year by overheated seawater. More southerly sections around the middle of the reef that barely escaped then are bleaching now, a potential precursor to another die-off that could rob some of the reef’s most visited areas of color and life.

“We didn’t expect to see this level of destruction to the Great Barrier Reef for another 30 years,” said Terry P. Hughes, director of a government-funded center for coral reef studies at James Cook University in Australia and the lead author of a paper on the reef that is being published Thursday as the cover article of the journal Nature. “In the north, I saw hundreds of reefs — literally two-thirds of the reefs were dying and are now dead.”

The damage to the Great Barrier Reef, one of the world’s largest living structures, is part of a global calamity that has been unfolding intermittently for nearly two decades and seems to be intensifying. In the paper, dozens of scientists described the recent disaster as the third worldwide mass bleaching of coral reefs since 1998, but by far the most widespread and damaging.

The state of coral reefs is a telling sign of the health of the seas. Their distress and death are yet another marker of the ravages of global climate change.

If most of the world’s coral reefs die, as scientists fear is increasingly likely, some of the richest and most colorful life in the ocean could be lost, along with huge sums from reef tourism. In poorer countries, lives are at stake: Hundreds of millions of people get their protein primarily from reef fish, and the loss of that food supply could become a humanitarian crisis.

With the international effort to fight climate change at risk of losing momentum, “ocean temperatures continue to march upward,” Dr. Cobb said. “The idea that we’re going to have 20 or 30 years before we reach the next bleaching and mortality event for the corals is basically a fantasy.”